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sobol

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  2. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    I have fixed my ps, P1 was wrongly soldered. I have believed that pin order in pcb is correct... it's not.


    Why do you add a switch to force the output to the positive unregulated voltage?
    Don't you want a switch to force the output to 0V?
    Then add a switch to the input of U2 and ground.


    Inverting or non-inverting input?

  5. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted


    R7 is 0.47 0hms and is in series with the load. Load current causes a voltage drop across R7. 3A x 0.47 ohms= 1.41V. With a low load current then the voltage across R7 is very low.
    The voltage across R7 is fed to pin 2 input of U3.

    U3 is used as a comparator. Normally its output is high so the LED is turned off and D9 does not reduce the output voltage.
    When the voltage across R7 exceeds the voltage of P2 then the output of U3 goes low enough to reduce the output voltage so that the load current is reduced to the setting of P2.

    Your U3 is not detecting the voltage across R7, it acts like an on-off switch. Maybe R7 is the wrong value or is connected wrong.

    What is the part number of your opamps?


    TLE2141IP opamps.

    So...
    R7 looks good to me, its 0,47ohm, 10W resistor, connected from the GND "cross" on the pcb to the output GND pad.
    I've checked this U3 and it works in weird way. As i wrote before, voltage on the 3rd pin of U3 changes from 0 to 1,3V depending on P2 position. BUT on the 2nd pin of U3 is 20mV to 30mV (depends on P1 position), and at 30mV current limiting turns on(while P2 sets 1,3V on pin 3). That 2nd pin voltage was measured between "Cross" ground and 2nd pin. It should work as comparator, but it's not, and I don't have any idea why.

  6. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    Power supply is soldered on normal PCB.
    OK, I've made some measurements, look at the result:

    U1 pin 6 (output) - 11.2V.
    U3 pin 3 - varies from 0 to 1.3V, depends on P2 position.
    10V zener diode works properly, there is 29V on emitter of Q3 while current limiter works, and 29V on pin 7 of U3.
    U3 pin 6 - 29V while current limiting off, -1V while current limiting on.

    And still power supply does not work properly. Any ideas? Can't see any bad soldering or something like that.

  7. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted


    Which version? The original, a modified one or the latest modification?
    Which transformer? 24VAC, 28VAC or 30VAC?
    Which opamps? TL081, MC34071 or TLE2141?


    Version from the first post (latest i believe), 28VAC transformer, TLE2141 opamps.


    The output should be able to go from calibrated 0V to calibrated 30.0V.
    Measure the output voltage of U1. It should be about 11.2V. The output amplifier has a calibrated gain of 2.68 times to make the output 30.0V max.

    I'll check it tomorrow and i'll post measurements.


    Your current regulator U3 is not working correctly. Its output should be high (so that D9 cannot reduce the output voltage and does not turn on the LED) until the load current in R7 causes as voltage drop that is more than the amount of voltage set by P2. 


    I'll focus on the U3 neighbourhood, maybe I will find a mistake.


    If you used DIP 14 pins case opamps then their maximum allowed dissipation is 1000mW when the anbient is 25 degrees C.
    The MC34071 will dissipate a maximum of 302mW and the TLE2141 will dissipate a max of 470mW. Not too hot.


    If its ok, i'm ok too. : D

  8. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    So, I have built that power supply, but after test run i've found what follows:

    P1 (voltage control pot) - without a load on the output i've got 7mV to 5V, and at maximum pot position current limiting turns on (while P2 is on the maximum, while less, current limiting is constantly turned on and output voltage is about -200mV).
    U1 gets too hot in my opinion - after 10 minutes of test run it was about 80-90 celsius degrees.

    Any ideas what could be wrong?

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